The present invention relates to an input device for a computer system. More specifically, the present invention relates to an input device for providing position information to the computer system based on movement of the input device.
A traditional computer input device, such as a mouse, includes a housing, with a ball mounted in the housing. The ball is either configured in a traditional manner in which, in the normal work position, the ball engages a work surface and rotates based on the user's movement of the mouse across the work surface. The ball may also be provided as a track ball, which is rotated by digital manipulation from the user. In either case, position encoders are used to detect rotation of the ball in the mouse, and to provide position information indicative of that rotation to the computer. In many instances, the position information is used to control movement of a visual image (such as a mouse cursor) on the display screen of the computer.
Also, in one prior device, a mouse is configured with the track ball arrangement described above. The track ball is preprinted with a uniform predetermined image. A charge coupled device is used to detect the image on the track ball and detect movement of the image. Movement of the predefined image is used to provide position information to the computer.
However, the prior computer mouse which uses the charge coupled device configuration has a number of significant disadvantages. First, the reaction time of charge coupled devices is quite slow. In addition, processing an image signal from a charge coupled device is computationally intensive and takes a relatively large, and expensive processor. Also, charge coupled devices are highly sensitive to saturation. In other words, if the ambient light conditions are variable, charge coupled devices do not perform well. In addition, if an extraneous light source, such as a relatively bright light, is directed toward the image producing surface, the charge coupled devices can easily become saturated and their performance then quickly degrades.
Further, another prior computer mouse commercially available from Mouse Systems of CA included a mouse with an LED which was used in conjunction with a mouse pad having a predetermined, uniform pattern thereon. The pattern was formed by a uniform grid of blue and red lines. The emissions from the LED was reflected off of the mouse pad to a detector which provided an analog output signal. The signal was in the form of a waveshape with peaks corresponding to the different colored grid lines. From this waveform, the lines were counted and interpolated to obtain position information. Such a mouse system requires a mouse pad with a special uniform pattern implemented thereon.
In addition, typical mouse pointing devices are operated using a fixed scale and resolution. A fixed scale means that the mouse must always be moved a given distance over a work surface in order to move the cursor image on the computer screen a given number of pixels. For example, in order to move the cursor by 200 pixels on a computer screen having a resolution of 200 dots per inch (dpi), the mouse must be moved a fixed distance over the work surface, such as two inches. Each time the mouse is moved two inches, no matter what surface it is moved over, that movement will always correspond to movement of the cursor image by 200 pixels.
Fixed resolution refers to the resolution of the computer screen for which the smallest detectable discrete movement of the mouse will change the cursor position on the computer screen by only a single pixel. For example, some conventional mice have a resolution generally in the range of 200-400 dpi. This means that the smallest discrete movement of the mouse which is detectable by the position encoding mechanism in the mouse will change the cursor position on the display screen by only a single pixel for screens having a resolution in the range of 200-400 dpi. However, if the computer screen has a higher resolution, such as 1200 dpi, the smallest detectable discrete movement of the mouse may cause the cursor image to move 4-6 pixels on the display screen. Some current mice, with highly accurate position encoding mechanisms, can achieve a resolution of 1200 dpi.
As stated above, the scale and resolution of conventional mouse pointing devices are fixed. In order to change the scale or resolution, the user is typically required to load a different mouse driver which modifies the behavior of the mouse to change the resolution or to change the scale. Alternatively, a user can also use a separate control panel applet to trigger the software device driver to change the scale and resolution. Using a control applet to change scale or resolution can be quite cumbersome.
In some applications, items to be selected on the screen are quite small. Therefore, it can be difficult to select items when a high resolution monitor is used. In some instances, a single pixel offset can change the selection from one targeted item (or option) to another. One method which can be used to overcome this difficulty in such applications is to maintain the resolution and magnification of the computer screen at its nominal level and to decrease the resolution of the pointing device. However, as indicated above, conventional methods for changing the resolution of the pointing device can be quite cumbersome, particularly when a user desires to change the resolution a number of times while operating within a single application.